Nat Rothschild wants to return to the board of Bumi Plc but the Bakrie family co-founders say they will tear up a deal to withdaw from the coal mining group if Rothschild continues his campaign. Photograph: Reuters

Indonesia's Bakrie family has threatened to tear up an offer to withdraw from Bumi plc, the coal mining group they co-founded with Nat Rothschild, if the financier continues his efforts to return to the company's board.

The Bakries – who as part of an increasingly acrimonious dispute with the banking scion proposed in October they would sever ties between their Indonesian businesses and the London-listed group – also said they would use "all legal means" to enforce an agreement that allows them to appoint key Bumi positions, including the chairman and chief executive.

Last week Rothschild called for a shareholder meeting to vote on a proposal which would see him return to a newly formed board following the ousting of 12 of 14 board members. The dispute centres around allegations of irregularities at the group's Indonesian coal mines.

The news came as independent shareholder Taube Hodson Stonex Partners became the latest to support Rothschild's proposal. Schroders and Sofaer Capital have also backed the financier and the outcome is looking increasingly close.